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United States Patent |
5,627,100
|
Maurel
,   et al.
|
May 6, 1997
|
Method for the making of surface-emitting laser diodes with mechanical
mask, the apertures having inclined flanks
Abstract
A method for making a set of surface-emitting laser diodes comprises the
making of reflectors by the epitaxial growth of at least one semiconductor
material through a mask having apertures with inclined flanks. This method
leads to the obtaining of the Bragg reflectors obtained in situ, removing
the need for the ion etching of a semiconductor substrate followed by a
phase for the conditioning of the surface of the sample before the
preparation of the desired laser structure.
Application: optical power source.
Inventors:
|
Maurel; Philippe (Sevres, FR);
Garcia; Jean-Charles (Athis-Mons, FR);
Hirtz; Jean-Pierre (L'Haye Les Roses, FR)
|
Assignee:
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Thomson-CSF (Paris, FR)
|
Appl. No.:
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524907 |
Filed:
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September 7, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
438/32; 117/105; 438/34; 438/39; 438/943 |
Intern'l Class: |
H01R 021/22 |
Field of Search: |
437/948,155,35,36
148/DIG. 102,DIG. 103,DIG. 104,DIG. 105,DIG. 106
|
References Cited
U.S. Patent Documents
4217597 | Aug., 1980 | Hirtz.
| |
4236122 | Nov., 1980 | Cho et al.
| |
4286238 | Aug., 1981 | Ursenbach.
| |
4394182 | Jul., 1983 | Maadox, III | 437/36.
|
4445130 | Apr., 1984 | Poulain et al.
| |
4485391 | Nov., 1984 | Poulain et al.
| |
4494237 | Jan., 1985 | Di Forte Poisson et al.
| |
4910168 | Mar., 1990 | Tsai | 148/DIG.
|
4950622 | Aug., 1990 | Kwon et al. | 437/129.
|
5001719 | Mar., 1991 | Trussel.
| |
5012476 | Apr., 1991 | Razeghi et al.
| |
5106823 | Apr., 1992 | Creuzet et al.
| |
5138407 | Aug., 1992 | Hirtz et al.
| |
5272106 | Dec., 1993 | Hirtz et al.
| |
5273929 | Dec., 1993 | Hirtz et al.
| |
5328854 | Jul., 1994 | Vakhshoori et al. | 437/35.
|
5378658 | Jan., 1995 | Toyoda et al. | 437/228.
|
5427983 | Jun., 1995 | Ahmad et al. | 148/DIG.
|
Foreign Patent Documents |
0369856 | May., 1990 | EP.
| |
Other References
Applied Physics Letters, vol. 61, No. 13, Sep. 28, 1992, pp. 1487-1489;
Donnelly, J. P., et al.; High Quantum Efficiency Monolithic Arrays of
Surface-Emitting Algaas Diode Lasers With Dry-Etched Vertical Facets and
Parabolic Deflecting Mirrors'.
|
Primary Examiner: Breneman; R. Bruce
Assistant Examiner: Paladugu; Ramamohan Rao
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
What is claimed is:
1. A method for the making of an optoelectronic power device that emits
coherent light given by a plurality of surface-emitting elementary lasers,
wherein said method comprises the following steps:
the making, through a mechanical mask with apertures having inclined
flanks, of reflectors by the epitaxial growth of at least one
semiconductor material, said reflectors having flanks that form an angle
.theta. with the plane of the substrate on which they are made;
the growth by selective epitaxy of the constituent layers of the laser
structure on said reflectors.
2. A method for the making of an optoelectronic device according to claim
1, wherein:
in a first stage, the growth of reflectors made of a semiconductor material
(I) is obtained through the mechanical mask,
in a second stage, after the removal of the mask in situ, the growth of
Bragg mirrors is obtained by operations of selective epitaxy of (A) and
(B) semiconductor materials.
3. A method for making an optoelectronic device according to claim 1,
wherein the growth of the Bragg mirrors is obtained through the mechanical
mask by operations of selective epitaxy of (A) and (B) semiconductor
materials on a plane substrate.
4. A method for making an optoelectronic device according to claim 1,
wherein the substrate is made of GaAs.
5. A method for making an optoelectronic device according to claim 2,
wherein the material (A) is GaAs and the material (B) is GaAlAs.
6. A method for making an optoelectronic device according to claim 2,
wherein the material (I) is GaAs.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of optoelectronic power devices, the
active part of which is constituted by an integrated circuit assembling a
plurality of semiconductor lasers.
More specifically, this integrated circuit brings together a plurality of
elementary lasers capable of generating power in the range of one watt and
hence capable of having optical sources of power of nearly one kilowatt.
Typically, these elementary lasers are associated in mutually parallel
linear arrays or strips on the chip of semiconductor material. The arrays
are raised with respect to the surface of the substrate in such a way that
they have two raised faces needed for the operation of each elementary
laser. These faces are parallel to the surface of the substrate. Two sets
of mirrors, positioned between the laser arrays, reflect the light beams
at 90.degree. and send them back perpendicularly to the surface of the
substrate. These mirrors are generally formed by the machining of the
substrate in planes inclined at 45.degree. and are then covered with at
least one metal layer that is used both as an optical reflector and as an
electrical conductor. In general, a first contact-making metallization is
deposited on each laser array (M.sub.e) and a second contact-making
metallization (M.sub.R) is deposited on each reflector. All the flanks of
the reflectors are also covered with a metallization (M'.sub.R) to provide
said reflective elements with high reflecting capacity. FIG. 1 shows a
view in perspective of an exemplary integrated circuit with
surface-emitting lasers. The metallised flanks of the 45.degree.
reflectors give rise to the desired surface emission.
2. Description of the Prior Art
In the prior art, the reflectors are generally obtained through etching by
the ion machining of a substrate made of semiconductor materials of the
III-V group. Then, in a second stage, deposits are made by epitaxial
growth of the successive layers need to prepare the laser structure.
This type of method then includes a phase, which is always a difficult one,
of conditioning the surface of the sample in order to prepare the renewal
of epitaxial growth of the laser structure on the etched substrate.
In order to avoid this step of ion machining followed by the renewal of
epitaxial growth of the laser structure on the 45.degree. reflectors that
are formed beforehand, the invention proposes a method of manufacture
enabling the preparation of Bragg reflectors forming an angle .theta. with
the substrate (this angle could be typically equal to about 45.degree.).
This is done through selective epitaxial growth by means of a mechanical
mask. The making of such reflectors then makes it possible to eliminate
the subsequent step of metallization of the reflectors as practised in the
prior art. This is always a difficult step if it is desired not to damage
the active faces of the laser structures, for these faces are very close
to the reflecting flanks.
SUMMARY OF THE INVENTION
More specifically, an object of the invention is a method for the making of
an optoelectronic power device that emits coherent light given by a
plurality of surface-emitting elementary lasers, wherein said method
comprises the following steps:
the making, through a mechanical mask with apertures having inclined
flanks, of reflectors by the epitaxial growth of at least one
semiconductor material, said reflectors having flanks that form an angle
.theta. with the plane of the substrate on which they are made;
the growth by selective epitaxy of the constituent layers of the laser
structure on said reflectors.
The desired angle .theta. may be adjusted by the distance between the
mechanical mask and the plane of the substrate.
In the method according to the invention, it is thus possible, in a first
stage, to achieve the growth of reflectors made of a semiconductor
material (I) through the mechanical mask and then, in a second stage,
after the removal of the mask in situ, to obtain the growth of Bragg
mirrors by the selective epitaxy of (A) and (B) semiconductor materials.
According to another alternative, it is also possible, directly through the
mechanical mask, to achieve the growth of Bragg mirrors by selective
epitaxy of (A) and (B) semiconductor materials on the plane substrate.
It is then possible, in a second stage, to eliminate the laser structure at
the Bragg mirrors so as to leave said laser structure only on the
substrate elements inserted between two Bragg mirrors.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be understood more clearly and other advantages shall
appear from the following description, which is given by way of a
non-restrictive example, and from the appended figures, of which:
FIG. 1 shows a comprehensive view of an optoelectronic power device that is
an emitter of coherent light given by a plurality of surface-emitting
elementary lasers;
FIG. 2 illustrates a step of the method for making devices similar to the
device shown in FIG. 1, using a mechanical mask to prepare the Bragg
mirrors;
FIG. 3 illustrates another example of a method according to the invention,
wherein the Bragg mirrors are made on a substrate prepared by epitaxy
through a mechanical mask;
FIG. 3a gives a schematic view of the making of the reflectors through the
mechanical mask;
FIG. 3b gives a schematic view of the making of the Bragg mirrors on the
previously formed reflectors;
FIG. 4 illustrates a step of ion etching at the end of the method, that can
be used to make wells needed to prepare the laser structures;
FIG. 5 illustrates a sub-etching step following the step illustrated in
FIG. 4:
FIG. 5a gives a schematic view of a sub-etching step of chemical corrosion,
FIG. 5b gives a schematic view of a step for the machining of the "struts"
obtained at the end of the previous step;
FIG. 6 illustrates a set of laser diodes obtained according to the method
of the invention.
MORE DETAILED DESCRIPTION
The method according to the invention for making an optoelectronic device
comprising surface-emitting laser elements preferably uses a substrate
made of group III-V materials. The materials used may typically be GaAs or
InP. Starting with such a substrate and using a mechanical mask with
controlled geometry, having apertures with optical flanks as shown
schematically in FIG. 2, it is possible, by adjusting the ratio between
the aperture and the distance of the mask, to make trapezoidal structures
with flanks that may be typically at an angle of 45.degree. with respect
to the substrate. It is thus possible, by means of alternating deposits of
semiconductor materials such as GaAlAs and GaAs, to make layers with a
thickness equal to a quarter of the wavelength of the semiconductor laser
that is subsequently made. Typically, in the case of lasers emitting at
0.8 .mu.m, the constituent layers of the Bragg reflectors have a thickness
of about 0.2 .mu.m. The reflective elements thus prepared may
advantageously have a height in the region of 20 .mu.m.
It is also possible to make reflectors with Bragg mirrors in two stages.
That is, it is possible, in a first stage, to make a reflector of GaAs
type material through a mechanical mask such as the one described here
above. Then, in a second stage, the mechanical mask may be removed in situ
to prepare the alternation of GaAs/GaAlAs layers by selective epitaxy,
making it possible to obtain the desired Bragg mirrors (FIGS. 3a and 3b).
The last constituent layer of the Bragg may typically be made of GaAlAs and
may thus also play the role of a so-called barrier layer in the
sub-etching step described here below.
In both examples, there is a set of reflectors having flanks forming an
angle .theta. with the substrate.
It is then possible to achieve the in situ growth of the laser structure on
the substrate comprising the Bragg reflectors.
In a first stage, it is possible to deposit a thick (about 6 .mu.m thick)
layer (C.sub.I) of GaAs capable of being etched by a solution that does
not corrode GaAlAs.
Then a sequence of the following is made: optical confinement layers
(C.sub.II) made of GaAlAs, a set of layers (C.sub.III).sub.i needed for
the laser structure proper made by prior art methods, a second confinement
layer (C.sub.IV) made of GaAlAs.
Ion etching is then used to make wells locally up to the layer (C.sub.I) as
shown in FIG. 4.
Thus, by chemical etching with a selective solution (of the citric acid,
H.sub.2 O.sub.2, H.sub.2 O type), sub-etching is carried out to make the
"struts" such as those shown in FIG. 5a. In a last stage, ion etching is
used to eliminate the overhanging parts (FIG. 5b).
Thus, a set of surface-emitting laser diodes is obtained. The thickness
e.sub.L of these diodes, shown in FIG. 6, is preferably smaller than that
of the reflectors having thicknesses e.sub.r, so as to recover the
divergent emission of said diodes as efficiently as possible. This
divergent emission, typically e.sub.L, may be in the range of 12 .mu.m if
e.sub.r is in the range of 20 .mu.m. In these examples, the width 1 of the
reflectors may typically be in the range of 40 to 50 .mu.m.
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